PART III- Voltage Surges, Over- voltages, Circuit Interrupters and Grounding Practices
Chapter 19. Circuit interrupters and their applications
• Circuit interrupters
• Theory of circuit interruption with different switching mediums
(theory of deionization)
• Theory of arc plasma
• Circuit breaking under unfavorable operating conditions
• Circuit interruption in different mediums
• HV and LV vacuum contactors
• Current chopping
• Virtual current chopping
• Containing the severity of switching surges
• Comparison of interrupting devices
• Gas insulated switchgears (GIS)
• Retrofitting of old installations
An interrupter is the electrical part and constitutes the switching device of a breaker. The operation of this device causes switching surges when closing or opening a circuit. Details of such surges and causes of their generation are discussed in chapter 17.
Surges that may appear on the LV side of a power system as a result of transference from the HV side of a transformer (Section 18.5.2) are different and not related to switching. Surges on the LV side due to switching of static devices (Section 6.13) are not related to the switching of the circuit but to the static devices themselves.
In this chapter we discuss the types of insulating and quenching mediums, their switching characteristics and merits and demerits of their use. We also consider the basic interrupting devices developed over the years, using such mediums, keeping switching surges as the basic criteria in mind. The theory of arc interruption is the same for all switching devices. The following types of breakers have been developed for the purpose of switching and they mostly relate to the HV systems, except where noted:
1. Bulk Oil Circuit Breakers (BOCBs)
2. Minimum Oil or Low Oil Content Circuit Breakers (MOCBs or LOCBs)
3. Air Circuit Breakers (ACBs) – generally for an LV system only
4. Air Blast Circuit Breakers (ABCBs)
5. Sulphur Hexafluoride Circuit Breakers (SF6 breakers)
6. Vacuum Circuit Breakers (VCBs)7 HV and LV Vacuum Contactors (VCs). Contactors are not breakers but covered here to comprehend the applications of vacuum interrupters as the contactors too embody an interrupting device.